Square skull is not necessarily rickets; square skull can be seen in rickets and congenital syphilis, especially common in rickets. It is often seen in children with rickets older than 8-9 months, due to a lack of calcium in the bones which leads to inadequate bone deposition and calcification. Under the periosteum of the child's frontal bone, parietal bone, and occipital bone, a large amount of osteoid deposition forms the square skull. Therefore, while square skull is not necessarily indicative of rickets, it is a common manifestation in rickets.